Field of the Invention
This invention relates to cardiac catheterization. More particularly, this invention relates to improvements in detecting complications of cardiac catheterization.
Description of the Related Art
The meanings of certain acronyms and abbreviations used herein are given in Table 1.
TABLE 1Acronyms and AbbreviationsMRIMagnetic Resonance ImagingECGElectrocardiogram
Cardiac arrhythmias, such as atrial fibrillation, occur when regions of cardiac tissue abnormally conduct electric signals to adjacent tissue, thereby disrupting the normal cardiac cycle and causing asynchronous rhythm.
Procedures for treating such arrhythmias include surgically disrupting the origin of the signals causing the arrhythmia, as well as disrupting the conducting pathway for such signals. By selectively ablating cardiac tissue by application of energy via a catheter, it is sometimes possible to interrupt or modify the propagation of unwanted electrical signals from one portion of the heart to another. The ablation process destroys the unwanted electrical pathways by formation of non-conducting lesions.
Verification of physical electrode contact with the target tissue is important for controlling the delivery of ablation energy while avoiding excessive contact force that might cause damage to the cardiac tissues. Attempts in the art to verify electrode contact with the tissue have been extensive, and various techniques have been suggested. For example, U.S. Pat. No. 6,695,808 describes apparatus for treating a selected patient tissue or organ region. A probe has a contact surface that may be urged against the region, thereby creating contact pressure. A pressure transducer measures the contact pressure. This arrangement is said to meet the needs of procedures in which a medical instrument must be placed in firm but not excessive contact with an anatomical surface, by providing information to the user of the instrument that is indicative of the existence and magnitude of the contact force.
In an invasive procedure performed on the heart, particularly a procedure involving mapping and ablation, there is a concern that the myocardial wall may be perforated, leading to unwanted entry of blood into the pericardial sac (hemopericardium) and development of a life threatening cardiac tamponade. Such a perforation is typically small. However, the flow rate of blood from the ventricular or atrial chamber into the pericardial space varies from low to high. Accordingly, it may take from a few minutes to a number of hours before the existence of the perforation is apparent.
A detailed description of the pericardial anatomy is given in the document Cardiac MRI: Part 2, Pericardial Diseases, Prabhakar Rajiah, American Journal of Roentgenology. October 2011; Vol. 197:W621-W634 (Rajiah), which is herein incorporated by reference. As is explained in Rajiah, the so-called “black blood” magnetic resonance imaging (MRI) technique may include weighted T1 and T2 sequences. The technique is useful to visualize normal pericardial anatomy, as well as effusions of blood into the pericardial sac. The black blood technique is a spin-echo MRI mode, in which high-velocity signal loss occurs. The technique employs excitation and refocusing pulses, which are 90° out of phase. Blood flowing within the heart in a slice of interest at the time of the 180° pulse will not have received the 90° pulse. Therefore, there is no magnetization in the transverse plane of the slice to refocus to an echo, and only a dark area appears on the resulting image. Pericardial fluid, which is not in rapid motion, appears as a white band on the image.